Method of precipitating layers of semiconducting or insulating material from a flowing reaction gas or from a flowing dopant gas upon heated semiconductor crystals

ABSTRACT

Method of precipitating layers of semiconducting or insulating material from a flowing reaction gas, upon heated semiconductor crystals, or for doping such crystals from a flowing dopant gas, wherein totally constant or only gradually changing operational conditions are maintained. The method is characterized by the fact that all working phases are so carried out with constant operational conditions. During one-half of the time required therefor, the reaction gas is transported approximately tangentially from one side over the semiconductor crystals to be processed. During the other half of the required period the reaction gas is transported approximately tangentially from the opposite side over the semiconductor crystals to be processed.

United States Patent Folkmann et al.

METHOD OF PRECIPITATING LAYERS OF SEMICONDUCTING OR INSULATING MATERIALFROM A FLOWING REACTION GAS OR FROM A FLOWING DOPANT GAS UPON HEATEDSEMICONDUCTOR CRYSTALS Eduard Folkmann; Erich Pammer, both of Munich.Germany Inventors:

Assignee: Siemens Aktiengesellschait, Berlin, Germany Filed: Feb. 26,1970 Appl.N0.: 14,437

Foreign Application Priority Data Mar. I8, 1969 Germany ..P l9 13 676.6

US. Cl. ..1l7/201, 117/106 A, 118/48,

23/2235 Int. Cl. ..C0lb 33/02 Field of Search ..l l7/200, 201, 106 A;23/2235 [56] References Cited UNITED STATES PATENTS 3,293,074 12/1966Nickl ..1 17/106 A Primary ExaminerWilliam L. Jarvis Attorney-Curt M.Avery, Arthur E. Wilfond, Herbert L. Lerner and Daniel J. Tick {5 7]ABSTRACT Method of precipitating layers of semiconducting or insulatingmaterial from a flowing reaction gas, upon heated'semiconductorcrystals, or for doping such crystals from a flowing dopant gas, whereintotally constant or only gradually changing operational conditions aremaintained. The method is characterized by the fact that all workingphases are so carried out with constant operational conditions. Duringone-half of the time required therefor, the reaction gas is transportedapproximately tangentially from one side over the semiconductor crystalsto be processed. During the other half of the required period thereaction gas is transported approximately tangentially from the oppositeside over the semiconductor crystals to be processed.

2 Claims, 1 Drawing Figure Patented April 25, 1972 3,658,585

annannaanaawaame 3 I I'IIIIIIIIIIIIIUIIIII! I l "mill-III H l lu v I'IIIIIIIYIIIIIIIIIIIIIIII H1 mmamvawzwza METHOD OF PRECIPITATING LAYERSOF SEMICONDUCTING OR INSULATING MATERIAL FROM A FLOWING REACTION GAS ORFROM A FLOWING DOPANT GAS UPON HEATED SEMICONDUCTOR CRYSTALS Ourinvention relates to a method for precipitating layers of semiconductingor insulating material from a flowing reaction gas upon heatedsemiconductor crystals or for doping such crystals from a flowing dopantgas, whereby operational conditions at all times remain constant or onlygradually change.

During the precipitation of epitactic semiconductor layers onmonocrystalline semiconductor layers or during pyrolytic precipitationof silicon oxide and/or silicon nitride layers from a gaseous phase uponsuch crystals, it is difficult to obtain homogeneous layer thickness,particularly when simultaneously coating large numbers of semiconductorwafers. A depletion of the reaction gas occurs in the active substances,which heretofore was compensated by producing a turbulent current of thereaction gas causing a mixing of the exhausted consumed gas with thefresh gas. This required the use of baffle members or moving stirringwings or moving gas inlet nozzles. All these devices necessitateadditional, particularly moving bodies in the reaction vessel, whichestablish a particularly intensive contact with the reaction gas. Thisincreases the contamination danger for the precipitated layers as wellas to an increased possibility of undesired precipitations in thereaction vessel.

It is an object of our invention to prevent the inhomogeneity of theprecipitation, caused by a depletion of active components in thereaction gas, by the simplest possible means.

To this end, we carry out all operational phases with constantoperational conditions and transport the reaction gas approximatelytangential, across the semiconductor crystals to be processed, from oneside, during half the time required thereto, and during the remainingperiod from the opposite side.

The method can also be varied in a manner whereby operation is carriedout with repeatedly alternating flow directions, during the individualabove defined working phases. Incidentally, we wish to point out thatthe concept of constantly maintained operational parameter is to befollowed in its strictest sense and that it relates to the constancy ofall operational parameters which influence the final result. In thisconnection, the temperature conditions, the position of the wafers to betreated in the reaction vessel and the composition and rate of thereaction gas above all should be mentioned.

The technical execution of the individual measures which serve for theprecipitation of inorganic layers from semiconductor surfaces,respectively for doping semiconductor crystals from the gaseous phase,are known and need not be described in detail. In order to put themethod of the invention into effect it is only necessary that therespective process be carried out with constantly maintained operationalconditions, either during the entire time which is needed or that saidprocess is comprised of individual steps which are maintained atconstant conditions which, however, vary from one another.

The invention provides that each step effected with constant conditionsbe carried out at an alternating flow direction of the reaction gas, asdescribed above. As a rule, it is sufficient that during the first halfof the time required for each of the steps, the reaction gas be suppliedfrom one direction while during the second half of the time required thereaction gas is transported from the opposite direction. However, aspreviously mentioned, it is sometimes expedient to change the flowdirection many times during individual phases. Care must be takenthough, that the total periods during which the gas is transported fromdifferent directions across the semiconductor wafers to be processed,equal each other during each of the working steps, as well as during theentire process.

The invention will be further described with respect to the drawing,which illustrates apparatus for carrying out the method.

The semiconductor wafers bemg treated are heated, to the necessaryprocessing temperature, by contact with an inductively heated plate 2 ofelectricity conducting material with a high thermal and chemicalresistance. The heating plate consists for example of a graphite bodywhose surface is completely coated, that is without spaces, with pureSiC or pure silicon. The heating plate 2 with the semiconductor wafersto be processed, is arranged in the interior of a quartz reaction tube.Each end of the tube is provided with a gas supply tube 4 or 5respectively. At the location of the heater 2, the tube is enclosedconcentrically by an induction coil. A forked tube 7 is provided for thesupply of gas, whose forks lead via a gas valve, respectively H H to agas inlet respectively, 4 or 5, entering the reaction tube. These gasinlets are so installed in the reaction tube that a current of gas flowsthereform, in opposite direction, approximately tangential across thesemiconductor wafers 1, being processed. In the example, both inlets arearranged at the ends of the reaction tube 3.

Each of the two gas inlets 4 and 5 is not only connected with the commongas lead 7, but also with an outlet, via another tube respectivelyprovided with a gas valve H or H,,. It thus becomes clear that it ispossible to transport the gas with this device, alternately in thedirection from the inlet 4 toward the inlet 5 which then serves as anoutlet, and vice versa. To this end, the gas valve pairs provided foreach of the two inlets 4 or 5, are kept selectively one open and oneclosed in such a way that, e.g. in one valve pair (H H or H H the valveis open for the outlet, while in the other, the valve 7 is open forcommon gas supply.

We claim:

1. The method of precipitating layers of semiconducting or insulatingmaterial from a flowing reaction gas, upon heated semiconductorcrystals, or for doping such crystals from a flowing dopant gas, whereintotally constant or only gradually changing operational conditions aremaintained, which comprises carrying out the working phases underconstant operational conditions, supplying approximately tangentiallythe reaction gas during one-half of the required time thereto, from oneside, while during the other half of the required time period from theopposite side, over the semiconductor crystals to be processed.

2. The method as claimed in claim 1, wherein during the individualphases of the constant operational conditions, the process is beingeffected with repeatedly changing flow direction.

2. The method as claimed in claim 1, wherein during the individual phases of the constant operational conditions, the process is being effected with repeatedly changing flow direction. 